Apparatus and method for a secure and diagnosable antijabber communication circuit

Abstract

In order to prevent `jabber`, the uncontrolled transmission of messages on a communication channel, an antijabber timing unit is frequently used to determine whether a message on the communication channel exceeds the maximum permitted length of time. The present invention provides testing apparatus to determine when the antijabber timing unit is functioning accurately. In addition, protection is provided so that the testing apparatus does not compromise the function of the antijabber timing unit during subsequent message transmission. The antijabber timing unit is also used as part of the enable function for the transmission of messages over a channel to prevent the failure of a single component from resulting in inadvertent transmission of information.

What is claimed is: 
     
       1. Apparatus for preventing uncontrolled communication in a process control network, said apparatus comprising: microprocessor means for providing a REQUEST signal, said REQUEST signal being generated during transmission of data signals by said microprocessor means and being generated during a test procedure; and   antijabber means responsive to said REQUEST signal for providing a LOCKED UP signal to said microprocessor means when said REQUEST signal exceeds a predetermined length, said LOCKED UP signal preventing transmission of data signals by said microprocessor means, said LOCKED UP signal causing said microprocessor means to apply an UNLOCK signal to said antijabber means after said REQUEST signal is removed during said test procedure, said UNLOCK signal causing microprocessor means to cancel said LOCKED UP signal, wherein said microprocessor means prevents transmission of data signals when said LOCKED UP signal is not generated during said test procedure.   
     
     
       2. The apparatus for preventing uncontrolled communication in a process control network of claim 1 further comprising logic means responsive to a simultaneous presence of said UNLOCK signal and said REQUEST signal to provide a RESET signal, said RESET signal being applied to said microprocessor means and causing said microprocessor means to halt operation and be reset. 
     
     
       3. The apparatus for preventing uncontrolled communication in a process control network of claim 2 wherein said logic means includes a logic AND gate having said UNLOCK signal applied to a first terminal and having said REQUEST signal applied to a second input terminal, wherein said logic AND gate provides said RESET signal to said microprocessor means when a REQUEST and an UNLOCK signal are simultaneously present. 
     
     
       4. The apparatus for preventing uncontrolled communication in a process control network of claim 3 wherein said REQUEST signal is an activation signal for permitting data signals to be transmitted to said process control network. 
     
     
       5. The apparatus for preventing uncontrolled communication in a process control network of claim 4 further comprising isolation means for reducing effects of single component failure on transmission of data signal over said process control network by providing a plurality of enabling signals for each of a plurality of communication channels. 
     
     
       6. The apparatus for preventing uncontrolled communication in a process control network of claim 5 wherein said isolation means includes signal means in said antijabber means for generating a WINDOW signal when said LOCKED UP signal is not present, wherein said REQUEST signal and said WINDOW signal enable communication from said microprocessor unit to said process control network. 
     
     
       7. Apparatus for preventing uncontrolled communication over a process control network, said apparatus comprising: microprocessor means for communicating data signals to said process control network;   antijabber timing means for applying a LOCKED UP signal to said microprocessor unit when said communicating data signals with said microprocessor means exceed a predetermined length of time, said LOCKED UP signal preventing said communicating data signals; and   testing means for verifying operation of said antijabber timing means, said testing means including first means in said microprocessor means for generating said REQUEST signal longer than said predetermined length of time during a test procedure, wherein said antijabber timing means provides said LOCKED UP signal after said predetermined length of time.   
     
     
       8. The apparatus for preventing uncontrolled communication over a process control network of claim 7 wherein said microprocessor means includes second means for identifying an antijabber timing means malfunction when said LOCKED UP signal is not generated during said test procedure. 
     
     
       9. The apparatus for preventing uncontrolled communication over a process control network of claim 8 wherein said testing means includes third means in said microprocessor means for providing an UNLOCK signal to said antijabber timing means when LOCKED UP signal is generated in response to said REQUEST signal during said test procedure, said UNLOCK signal causing said LOCKED UP signal to be removed by said antijabber timing means. 
     
     
       10. The apparatus for preventing uncontrolled communication over a process control network of claim 9 wherein said UNLOCK signal is applied to said antijabber timing means after said REQUEST signal has been removed during said test procedure. 
     
     
       11. The apparatus for preventing uncontrolled communication over a process control network of claim 10 further comprising logic means responsive to a simultaneous presence of said UNLOCK signal and REQUEST activation signal for applying a RESET signal to said microprocessor means, said RESET signal causing said microprocessor means to halt operation and to be reinitialized. 
     
     
       12. The apparatus for preventing uncontrolled communication over a process control network of claim 11 wherein said UNLOCK signal is generated after said REQUEST signal is removed in said test procedure. 
     
     
       13. The apparatus for preventing uncontrolled communication over a process control network of claim 12 further comprising enabling means, said enabling means including signal generating means associated with said antijabber means, said signal generating means providing a WINDOW signal, said WINDOW signal and said REQUEST signal enabling said communicating data signals with said microprocessor means. 
     
     
       14. A method for preventing uncontrolled communication over a process control network, said method comprising the steps of: generating REQUEST signal when a microprocessor unit transmits data signals to said process control network;   applying said REQUEST signal to an antijabber timing unit;   generating a LOCKED UP signal by said antijabber timing unit when REQUEST signal associated with said data signals exceeds a predetermined period;   applying said LOCKED UP signal to said microprocessor unit, said LOCKED UP signal identifying a jabber event;   periodically generating a test REQUEST signal exceeding said predetermined period, said test REQUEST signal being applied to said antijabber timing unit;   generating an UNLOCK signal by said antijabber timing circuit when a LOCKED UP signal is generated in response to said test REQUEST signal and applying said UNLOCK signal to said microprocessor unit, wherein said LOCKED UP signal is removed in response to said UNLOCK signal; and   preventing transmission of data groups to said process control network by said microprocessor unit when said LOCKED UP signal is not generated in response to said test REQUEST signal.   
     
     
       15. The method for preventing uncontrolled communication over a process control network of claim 14 further comprising the step of reinitiating transmission of data groups by said microprocessor unit when said test REQUEST signal and said UNLOCK signal are simultaneously present. 
     
     
       16. The method for preventing uncontrolled communication over a process control network of claim 15 further comprising the step of generating a WINDOW signal by said antijabber timing circuit when said LOCKED UP signal is not present, said WINDOW signal providing a separate signal for enabling transmission of said data signals to said process control network. 
     
     
       17. The method for preventing uncontrolled communication over a process control network of claim 16 further comprising the step of generating UNLOCK signal after removal of said REQUEST signal.